1. Field of the Invention
This invention relates to an insulating glass element for at least partial delimitation of a combustion chamber, having at least two viewing panes, which include in at least some areas a transparent glass or ceramic-glass material and which are spaced apart from each other while leaving an air chamber, and a viewing area is created at least in parts of the air chamber.
2. Discussion of Related Art
Insulating glass elements are used in connection with space heating devices, for example fireplaces, and other combustion installations, for example garbage-burning installations, pyrolysis furnaces, crematoria and the like, or also in ovens, for example as the oven door. They permit the user to view the combustion chamber. In the process, an insulating effect is achieved by the multi-pane construction.
A door for an oven is known from United Kingdom Patent Reference GB 1,087,296. It has two viewing panes, which extend parallel with respect to each other and are kept apart by spacing elements. Internal air can circulate in the air chamber thus formed and is heated while passing through the air chamber and aids in heating the chamber.
A door system is described in U.S. Pat. No. 4,058,107, which also has two viewing panes with spacing devices. The door frame contains a number of ventilating openings, both in the lower as well as the upper holding strip, so that the air heated in the space between the panes can move by convection and supply the operating space with warm air.
United States Patent Reference 2004 00 11 348 A1 describes a double-pane construction, which also defines a space between both viewing panes. However, the viewing panes are not arranged parallel to each other, but are constructed so that the gap at the upper end of the viewing panes is reduced. A blower additionally blows either room air or fresh air into the space between the panes, in particular for cooling the inner viewing panes, to achieve a temperature load under which prestressed soda-lime glass can be safely employed.
Finally, United States Patent Reference 2005/01 39 209 A2 goes still one step further, as described in United States Patent Reference 2004 00 11 348, where air is moved by convection, either without being forced, or with the aid of a blower, between the viewing panes. The outer viewing pane is replaced by a plastic pane. Electrical energy is required for operating the blower, which worsens the energy balance.
With known insulating glass elements, dust, and depending on the respective construction, soot, collects between the viewing panes, so that regular cleaning is required. Thus, respectively one of the viewing panes would have to be removably integrated in a holder. With only a small cost outlay, this is not possible with the known systems. Also, this requires an elaborate frame structure for the insulating glass element. In case of flare-ups in the combustion chamber, the viewing panes are subjected to large stresses. The forces thus created in case of a flare-up are transmitted via the spacing elements from the inner to the outer viewing pane. During this, pressure peaks are generated in the area of the spacing elements. In order to reduce these safely, the individual viewing panes must have sufficient strength, and therefore sufficient thickness.
One disadvantage regarding emission characteristics of the combustion location can be noted in connection with the known insulating glass elements. The viewing pane facing the combustion location is cooled by the circulating air. The generation of nitric oxide, for example, is aided at the inside of the cooled inner pane, which contributes to the worsening of the waste gas characteristics. Also, the combustion temperature is limited by cooling the inner pane, which leads to an increase in fine dust emissions.